Semiconductor light emitting device having a fluorescent material emitting light of a secondary wavelength

ABSTRACT

There are provided a semiconductor light emitting device wherein the variation in tone in each device is small and the variation in tone due to deterioration with age is also small, and a method for manufacturing the same. The semiconductor light emitting device includes an active layer for emitting primary light having a first wavelength by current injection, and a light emitting layer excited by the primary light for emitting secondary light having a second wavelength different from said first wavelength, wherein the primary light and the secondary light are mixed to be outputted.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional of application Ser. No. 09/803,457 filed Mar. 9,2001, now U.S. Pat. No. 6,576,933, which application is herebyincorporated by reference in its entirety.

This application claims benefit of priority under 35USC §119 to JapanesePatent Applications No. 2000-066736, filed on Mar. 10, 2000 and No.2000-396957, filed on Dec. 27, 2000, the entire contents of which areincorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a semiconductor lightemitting device and a method for manufacturing the same.

2. Related Background Art

In recent years, semiconductor white light emitting devices are widelynoticed as successors to incandescent lamps and fluorescent lamps. Sucha semiconductor white light emitting device is characterized by a simpledriving circuit and small electric power consumption.

As the semiconductor white light emitting devices, there are proposeddevices using GaN compound semiconductor light emitting elements (GaNcompound semiconductor white light emitting devices) and devices usingZnSe compound semiconductor light emitting elements (ZnSe compoundsemiconductor light emitting devices).

The GaN compound semiconductor white light emitting devices aredescribed in, e.g., Japanese Patent Laid-Open Nos. 10-242513, 10-12916and 11-121806.

The GaN compound semiconductor white light emitting device disclosed inJapanese Patent Laid-Open No. 10-242513 comprises a GaN compoundsemiconductor light emitting element for emitting blue light, and aYAG:Ce fluorescent material for absorbing the emitted blue light to emityellow light, to achieve white light by mixing the blue light emissionand the yellow light emission. The YAG:Ce fluorescent material is mixedin a resin to be applied to a portion surrounding the semiconductorlight emitting element.

The GaN compound semiconductor white light emitting device disclosed inJapanese Patent Laid-Open No. 10-12916 comprises a GaN compoundsemiconductor light emitting element for emitting ultraviolet light, andthree kinds of fluorescent materials for absorbing the emittedultraviolet light to emit red light, the green light and the blue light,to achieve white light by mixing red light emission, green lightemission and blue light emission. The fluorescent materials are mixed ina resin to be applied to a portion surrounding the semiconductor lightemitting element.

The GaN compound semiconductor white light emitting device disclosed inJapanese Patent Laid-Open No. 11-121806 comprises three kinds of activelayers including an active layer for emitting red light, an active layerfor emitting green light and an active layer for emitting blue light, toachieve white light by mixing the red light emission, the green lightemission and the blue light emission. The three kinds of active layersare separately provided, and a current is injected into each of theactive layers.

A ZnSe compound semiconductor light emitting device comprises a ZnSecompound semiconductor light emitting element for emitting blue light,and an emission center, formed on the substrate, for emitting yellowlight, to achieve white light by mixing the blue light emission and theyellow light emission.

However, as a result of the inventors' experimental manufacture andevaluation, it was found that, in the conventional semiconductor whitelight emitting devices, there are problems in that the tone of whitelight varies for each device and that the tone deteriorates with age, asfollows.

First, when a fluorescent material is mixed in a resin to be applied toa portion surrounding a semiconductor element as in the semiconductorwhite light emitting device disclosed in Japanese Patent Laid-Open No.10-242513, it is difficult to maintain the quantity of the fluorescentmaterial for each element at a constant level, so that the quantity ofthe fluorescent material varies for each device. For example, when thequantity of the fluorescent material is large, the intensity of emittedyellow light is high, so that the tone of white light is close toyellow. On the other hand, when the quantity of the fluorescent materialis small, the intensity of emitted yellow light is low, so that the toneof white light is close to blue. For that reason, the tone of whitelight varies for each device. In addition, since the fluorescentmaterial is deteriorates more easily than the semiconductor lightemitting element, the tone greatly deteriorates with age. For example,when the fluorescent material deteriorates to and the yellow lightemission weakens the tone is close to blue.

In addition, when three kinds of fluorescent materials are used as inthe semiconductor white light emitting device disclosed in JapanesePatent Laid-Open No. 10-12916, it is difficult to carry out a propermixing of the fluorescent materials, so that the compounding ratio ofthe fluorescent materials varies for each device. For example, when thequantity of the blue light emitting fluorescent material is large, thetone is close to blue. For that reason, the tone of white light variesevery device. Also, as in the case of the above described devices, thevariation in tone due to the variation in quantity of the fluorescentmaterials, and the variation in tone due to the deterioration of thefluorescent materials are easily caused.

In addition, in the structure wherein three kinds of active layers forred light emission, green light emission and blue light emission areused as in the semiconductor white light emitting device disclosed inJapanese Patent Laid-Open No. 11-121806 the light emission of each layervaries in accordance with the injected current, so that it is difficultto adjust the balance of light emissions of three colors. For example,when the current injected into the blue light emitting active layer istoo large, the tone of white light is close to blue. For that reason,the tone of white light varies.

Moreover, in the structure wherein an emission center is formed on thesubstrate as in the ZnSe compound semiconductor light emitting device,it is difficult to maintain the quantity of the emission center at aconstant level for each wafer, so that the quantity of the emissioncenter varies for each wafer. For example, when the quantity of theemission center is large, the quantity of emitted yellow light is large,so that the tone of white light is close to yellow. On the other hand,when the quantity of the emission center is small, the quantity ofemitted yellow light is small, so that the tone is close to blue. Forthat reason, the tone of white light varies.

Thus, it was found that, in the conventional semiconductor white lightemitting devices, there are problems in that the tone of white lightvaries for each device and that the tone deteriorates with age.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to eliminate theaforementioned problems and to provide a semiconductor light emittingdevice wherein the variation in tone is small and the deterioration oftone is slow.

In order to accomplish the aforementioned and other objects, accordingto one aspect of the present invention, there is provided asemiconductor light emitting device comprising: a semiconductor lightemitting element which has an active layer for emitting primary lighthaving a first wavelength by current injection; and at least onesemiconductor laminate which is bonded to said semiconductor lightemitting element and which has a light emitting layer, excited by saidprimary light, for emitting secondary light having a second wavelengthdifferent from said first wavelength, wherein said primary light andsaid secondary light are mixed to be outputted.

The active layer may be a In_(p)Ga_(q)Al_(1-p-q)N (0≦p≦1, 0≦q≦1,0≦p+q≦1) active layer. And the In_(p)Ga_(q)Al_(1-p-q)N active layerincludes, for example, an active layer having a multi-quantum wellstructure of InGaN and GaN. The light emitting layer may be anIn_(b)Ga_(c)Al_(1-b-c)P (0≦b≦1, 0≦c≦1, 0≦b+c≦1) light emitting layer.

According to another aspect of the present invention, there is provideda semiconductor light emitting device comprising: A semiconductor lightemitting device comprises: a GaAs substrate; an In_(b)Ga_(c)Al_(1-b-c)P(0≦b≦1, 0≦c≦1, 0≦b+c≦1) light emitting layer which is formed on saidGaAs substrate and which is excited by primary light having a firstwavelength for emitting secondary light having a second wavelength; abuffer layer formed on said In_(b)Ga_(c)Al_(1-b-c)P light emittinglayer; and a Zn_(j)Cd_(1-j)Se (0≦j≦1) active layer which is formed onsaid buffer layer and which emits said primary light having the firstwavelength by current injection; wherein said primary light and saidsecondary light are mixed to be outputted.

The Zn_(j)Cd_(1-j) Se active layer includes, for example, an activelayer having a multi-quantum well structure of ZnCdSe and ZnSe.

According to another aspect of the present invention, there is provideda method for manufacturing a semiconductor light emitting device, themethod comprising: a semiconductor light emitting element forming stepincluding a step of forming on a first substrate a semiconductor layers,which has an active layer for emitting primary light having a firstwavelength by current injection; a semiconductor laminate forming stepincluding a step of forming on a second substrate a semiconductorlayers, which includes a light emitting layer excited by said primarylight for emitting secondary light having a second wavelength differentfrom said first wavelength; and a bonding step including a step ofintegrally bonding said semiconductor light emitting element to saidsemiconductor laminate.

According to another aspect of the present invention, there is provideda method for manufacturing a semiconductor light emitting device, themethod comprising the steps of: forming on a GaAs substrate anIn_(b)Ga_(c)Al_(1-b-c)P (0≦b≦1, 0≦c≦1, 0≦b+c≦1) light emitting layer,which is excited by blue light for emitting yellow light; forming abuffer layer on said In_(b)Ga_(c)Al_(1-b-c)P light emitting layer; andforming on said buffer layer a ZnCe compound active layer, which emitssaid blue light by current injection.

According to a further aspect of the present invention, there isprovided a semiconductor light emitting device comprising: a substrate;a buffer layer formed on said substrate; a first conductive typeIn_(r)Ga_(s)Al_(1-r-s)N (0≦r≦1, 0≦s≦1, 0≦r+s≦1) cladding layer formed onsaid buffer layer, an In_(p)Ga_(q)Al_(1-p-q)N (0≦p≦1, 0≦q≦1, 0≦p+q≦1)active layer formed on said first conductive typeIn_(r)Ga_(s)Al_(1-r-s)N cladding layer and provided with an ionimplantation region into which ions selected from the group consistingof fluorine, oxygen, nitrogen, carbon and sulfur have been injected,regions other than said ion implantation region emitting primary lighthaving a first wavelength, and said ion implantation region emittingsecondary light having a second wavelength different from said firstwavelength; and a second conductive type In_(t)Ga_(u)Al_(1-t-u)N (0≦t≦1,0≦u≦1, 0≦t+u≦1) cladding layer formed on said active layer.

According to a still further aspect of the present invention, there isprovided a semiconductor light emitting device comprising: asemiconductor light emitting element which has an active layer foremitting primary light having a first wavelength by current injection;reflector for reflecting said primary light emitted from saidsemiconductor light emitting element; and fluorescent material which isapplied on part of said reflector and which is excited by said primarylight for emitting secondary light having a second wavelength differentform said first wavelength.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given herebelow and from the accompanying drawings of thepreferred embodiments of the invention. However, the drawings are notintended to imply limitation of the invention to specific embodiments,but are for the purpose of explanation and understanding only.

In the drawings:

FIG. 1 is a schematic sectional view of the first preferred embodimentof a semiconductor light emitting device according to the presentinvention;

FIG. 2 is a schematic sectional view showing a method for manufacturingthe first preferred embodiment of a semiconductor light emitting deviceaccording to the present invention;

FIG. 3 is a schematic sectional view showing a method for manufacturingthe first preferred embodiment of a semiconductor light emitting deviceaccording to the present invention;

FIG. 4 is a schematic sectional view of the second preferred embodimentof a semiconductor light emitting device according to the presentinvention;

FIG. 5 is a schematic sectional view of the third preferred embodimentof a semiconductor light emitting device according to the presentinvention;

FIG. 6 is a schematic sectional view showing a method for manufacturingthe third preferred embodiment of a semiconductor light emitting deviceaccording to the present invention;

FIG. 7 is a schematic sectional view of the fourth preferred embodimentof a semiconductor light emitting device according to the presentinvention;

FIG. 8 is a schematic sectional view of the fifth preferred embodimentof a semiconductor light emitting device according to the presentinvention;

FIG. 9 is a schematic sectional view of the sixth preferred embodimentof a semiconductor light emitting device according to the presentinvention;

FIG. 10 is a schematic sectional view of the seventh preferredembodiment of a semiconductor light emitting device according to thepresent invention;

FIG. 11 is a schematic sectional view of the eighth preferred embodimentof a semiconductor light emitting device according to the presentinvention;

FIG. 12 is a chromaticity diagram for explaining the chromaticity of theeighth preferred embodiment of a semiconductor light emitting deviceaccording to the present invention, which is an xy chromaticity diagramdefined by International Commission on Illumination (CIE);

FIG. 13 is a schematic sectional view of the ninth preferred embodimentof a semiconductor light emitting device according to the presentinvention;

FIG. 14 is a schematic sectional view of the tenth preferred embodimentof a semiconductor light emitting device according to the presentinvention;

FIG. 15 is a schematic sectional view of the eleventh preferredembodiment of a semiconductor light emitting device according to thepresent invention;

FIG. 16 is a characteristic diagram showing characteristic of a low-passfilter of the eleventh preferred embodiment of a semiconductors lightemitting device according to the present invention;

FIG. 17 is a schematic sectional view of the twelfth preferredembodiment of a semiconductor light emitting device according to thepresent invention;

FIG. 18 is a schematic sectional view of the thirteenth preferredembodiment of a semiconductor light emitting device according to thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Thirteenth kinds of preferred embodiments of the present invention willbe described below.

First, in each of the first through seventh preferred embodiments, therewill be described a semiconductor white light emitting device whichcomprises a semiconductor light emitting element for emitting blue lightby current injection, and a semiconductor laminate for transforming theblue light to emit light of another color, the semiconductor laminatebeing bonded substantially to the entire light emitting surface of thesemiconductor light emitting element or the entire opposite surface tothe light emitting surface. Among these embodiments, in each of thefirst through fifth preferred embodiments, a GaN compound semiconductorlight emitting element is used as the semiconductor light emittingelement, and in the each of sixth and seventh preferred embodiments, aZnSe compound semiconductor light emitting element is used as thesemiconductor light emitting element.

Then, in each of the eighth through eleventh preferred embodiments,there will be described a semiconductor white light emitting devicewhich comprises a GaN compound semiconductor light emitting element foremitting blue light, and a semiconductor laminate having a double-heterostructure for transforming the blue light to emit yellow light, thesemiconductor laminate being bonded to a part of the light emittingsurface of the GaN compound semiconductor light emitting element or apart of the opposite surface to the light emitting surface.

Moreover, in each of the twelfth and thirteenth preferred embodiments,there will be described another semiconductor white light emittingdevice relevant to the present invention.

Referring now to the accompanying drawings, the preferred embodiments ofa semiconductor light emitting device according to the present inventionwill be described below.

(First Preferred Embodiment)

FIG. 1 is a schematic sectional view showing the first preferredembodiment of a semiconductor white light emitting device according tothe present invention. A semiconductor light emitting element 1 foremitting blue light E1 by current injection and a semiconductor laminate2 excited by the blue light E1 for emitting yellow light E2 are bondedto each other at a bonding surface A to constitute a semiconductor whitelight emitting device. As can be seen from FIG. 1, these light beams areemitted from the top side in the figure.

First, the semiconductor light emitting element 1 will be described. Onthe top face of a sapphire substrate 104 in the figure, there aresequentially formed a buffer layer 105, an n-type GaN cladding layer(n-type contact layer) 106, an active layer 107 having a GaN/InGaNmulti-quantum well structure (MQW structure), a p-type AlGaN claddinglayer 108 and a p-type GaN contact layer 109. Furthermore, the “n-typeGaN cladding layer 106” will sometimes be referred to as the “n-typecladding layer 106” herein. The same applies to the other layers A partof the semiconductor light emitting element 1 is etched to expose then-type cladding layer 106 to form an n-side electrode 111 contacting then-type cladding layer 106. On the top of the p-type contact layer 109, ap-side transparent electrode 110 a is formed. The p-side transparentelectrode 110 a is made of a metal thin film or a conductive oxide film,and is capable of transmitting blue light E1 emitted from the activelayer 107 and yellow light E2 emitted from a light emitting layer 102.Thus the transparent electrode is used, the emission luminance of thedevice of FIG. 1 increases since the light emitting surface is arrangedon the p-type contact layer 109. On the top of the p-side transparentelectrode 110 a, a p-side electrode 110 is formed. A current is injectedfrom the p-side electrode 110 and the n-side electrode 111 to emit bluelight E1 from the active layer 107.

The semiconductor laminate 2 will be described below. The semiconductorlaminate 2 has a structure wherein the light emitting layer 102 of anInAlP/InGaAlP multilayer film is located between a GaAs substrate 101and an InAlP cladding layer (contact layer) 103. The GaAs substrate 101has a lattice constant close to that of the light emitting layer 102 ofan InAlP/InGaAlP multilayer film. Therefore, the GaAs substrate is usedfor carrying out the crystal growth, the crystalline characteristic ofthe light emitting layer 102 is improved to enhance the luminousefficiency. The GaAs substrate 101 is non-transparent with respect toyellow light E2 emitted from the light emitting layer 102 and blue lightE1 emitted from the active layer 107. However, since the GaAs substrate101 is arranged on the opposite side to the light emitting surface inthe device of FIG. 1, the emission luminance is high even if the GaAssubstrate 101 exists. For that reason, in the device of FIG. 1, the GaAssubstrate is not removed, so that the manufacturing process issimplified. Since the GaAs substrate 101 also has a smaller band gapthan the light emitting layer 102, the GaAs substrate 102 does not serveas the cladding layer of the light emitting layer 102. Therefore, in thesemiconductor laminate 2 of FIG. 1, the light emitting layer 102 is madeof the InAlP/InGaAlP multilayer film, so that electrons and holesgenerated by blue light E1 emitted from the semiconductor light emittingelement 1 can be confined in the light emitting layer 102. Thus thelight emitting layer 102 has the multilayer structure, the luminousefficiency of the emitted yellow light E2 is enhanced, so that theemission luminance of the emitted yellow light E2 increases. In FIG. 1the top face of the InAlP cladding layer 103 of the semiconductorlaminate 2 thus constructed is bonded to the bottom face of the sapphiresubstrate 104 of the semiconductor light emitting element 1 In thesemiconductor light emitting element 1 and semiconductor laminate 2described above, blue light E1 having a wavelength of 485 nm is emittedfrom the active layer 107 of the semiconductor light emitting element 1by current injection, a part of the blue light E1 emitted downward inthe figure is incident on the semiconductor laminate 2, and the incidentblue light E1 excites the light emitting layer 102 of the semiconductorlaminate 2 to cause it to emit yellow light E2 having a wavelength of590 nm. Thus, the blue light E1 emitted from the active layer 107 andthe yellow light E2 emitted from the light emitting layer 102 canrealize white light emission.

In the semiconductor white light emitting device of FIG. 1, the colortemperature of white light was about 8000 K, and the luminous intensityduring the injection of a current of 20 mA is 2 cd in a package having aradiation angle of 10 degrees. The color temperature of white light canbe controlled by adjusting the emission wavelengths and emissionintensities of the semiconductor light emitting element 1 andsemiconductor laminate 2. In the element structure of FIG. 1, thetransparent characteristic of the p-side transparent electrode 110 aalso has an influence on the color temperature and the luminousintensity. That is, since the p-side transparent electrode 110 atransmits light E1 and light E2 having different wavelengths, a requiredcolor temperature can be obtained by adjusting the transmittance foreach light.

In the semiconductor white light emitting device of FIG. 1 describedabove, it is possible to decrease the variation in tone for eachelement. Because the thickness and composition of the semiconductorlaminate 2 hardly vary for each element. That is, by using astandardized mass production process generally used for themanufacturing of semiconductor elements, the semiconductor laminate 2can be manufactured with high repeatability so that the thickness andcomposition hardly vary. Thus the thickness and composition of thesemiconductor laminate 2 are uniform for each element, the ratio of thequantity of the blue light E1 emitted from the semiconductor lightemitting element 1 to that of the yellow light E2 emitted from thesemiconductor laminate 2 does not vary for each device, so that the tonedoes not vary for each device.

In the semiconductor white light emitting device of FIG. 1, the tonehardly deteriorates with age, because the deterioration with age of theyellow light emitting semiconductor laminate 2 is smaller than that offluorescent lamps. Since the deterioration with age of the semiconductorlaminate 2 is small, the ratio of the quantity of the blue light E1emitted from the semiconductor light emitting element 1 to that of theyellow light E2 emitted from the semiconductor laminate 2 does not vary,so that the tone hardly vary.

Referring to FIGS. 2 and 3, a method for manufacturing the semiconductorwhite light emitting device of FIG. 1 will be described below. As shownin FIG. 2, one of the features of this manufacturing method is that alight emitting layer 103 is formed on a GaAs substrate 101 suitable forthe formation of the light emitting layer 103, and thereafter, this isbonded to a semiconductor blue light emitting device 1.

First, in the manufacturing of the semiconductor laminate 2, a GaAssubstrate (a second substrate) 101 is cleaned with an organic solventand/or a sulfuric acid containing etchant, and then, the GaAs substrate101 is introduced into an MOCVD system. Then, the GaAs substrate 101 isheated to 730° C., and an appropriate 5-Group material serving as a Pmaterial is supplied to sequentially grow a light emitting layer 102 ofan InAlP/InGaAlP multilayer film and an InAlP cladding layer 103.Further a GaAs cap layer 112 is grown on the surface thereof. The GaAscap layer 112 is a protection layer which is finally removed. Thethickness of these layers are shown in the following table 1.

TABLE 1 InAlP/InGaAlP Light Emitting Layer 102  30 nm/50 nm InAlPCladding Layer 103 300 nm or less GaAs Cap Layer 113 100 nm

Specifically, the light emitting layer 102 has a structure wherein 20InAlP layers having a thickness of 30 nm and 20In_(0.5)(Ga_(0.7)Al_(0.3))_(0.5)P layers having a thickness of 50 nm arealternately stacked. The InAlP cladding layer 103 serves as an adhesivelayer for bonding the semiconductor laminate 2 to the semiconductorlight emitting element 1, also serves and as a protection layer forprotecting the light emitting layer 102. At the same time it has thefunction of confining excitation carriers therein. Since the InGaAlPcontact layer absorbs emitted blue light E1, it preferably has athickness of 100 nm or less to reduce light loss due to the absorptionof blue light E1.

Then, in the manufacturing of the semiconductor light emitting element1, as can be seen from FIG. 3, a sapphire substrate (a first substrate)104 is cleaned with an organic solvent and/or a sulfuric acid containingetchant, and then, is introduced into the MOCVD system. Then, after thesapphire substrate 104 is thermally cleaned at 1100° C., a buffer layer105, an n-type GaN cladding layer 106, a GaN/InGaN active layer 107 ofthe MQW structure, a p-type AlGaN cladding layer 108 and a p-type GaNcladding layer 109 are sequentially formed. The growth temperature andthickness of these layers are shown in Table 2.

TABLE 2 Buffer Layer 105  500 ° C.  30 nm n-type GaN Cladding Layer 1061050 ° C.  4 μm GaN/InGaN Active Layer 107  750 ° C.  7 nm/3 nm p-typeAlGaN Cladding Layer 108 1050 ° C.  50 nm p-type GaN Contact Layer 1091050 ° C. 150 nm

Specifically, the active layer 107 has a 5QW structure of anIn_(0.35)Ga_(0.65)N layer having a thickness of 3 nm and a GaN layerhaving a thickness of 7 nm.

Then, the semiconductor light emitting element 1 and the semiconductorlaminate 2 thus manufactured are bonded to each other. Before bonding,the GaAs cap layer 112 formed on the semiconductor laminate 2 as theprotection layer is etched to be removed with a sulfuric acid containingetchant. After the GaAs cap layer 112 is removed, the surface of theInAlP cladding layer 103 is subsequently cleaned. With respect to thesemiconductor light emitting element 1, the bottom side of the sapphiresubstrate 104 in FIG. 3 is mirror-polished and simultaneously trimmed toform a flat surface. In order to facilitate the element isolation whichwill be carried out later, the trimming was carried out so that thewhole thickness of the semiconductor light emitting element 1 is about100 μm.

Then, the bottom side of the sapphire substrate 104 of the semiconductorlight emitting element 1 in FIG. 3 is aligned with the top side of theInAlP cladding layer 103 of the semiconductor laminate 2 in FIG. 2.Specifically, after the semiconductor light emitting element 1 isaligned with the semiconductor laminate 2, they are annealed at 500° C.in an atmosphere of nitrogen for 30 minutes to be bonded to each otherby a dehydrating condensation reaction. In order to improve adhesion,the surfaces to be bonded are preferably as flat as possible. In theplanarization of the InAlP cladding layer 103 of the semiconductorlaminate 2, the GaAs substrate 101 inclined in a direction of [011] fromthe plane (100) is effectively used. In FIG. 2, the GaAs substrate 101inclined at 15° is used so that the surface roughness of the top side ofthe InAlP cladding layer 103 in the figure is about 2 nm. The surfaceroughness of the bottom side of the sapphire substrate 104 in FIG. 3 ismade 20 nm or less by the mirror polishing.

Then, as can be seen from FIG. 1, a part of the semiconductor lightemitting element 1 is etched from the p-type contact layer 109 to then-type cladding layer 106, and then, n-side electrode 111, a p-sidetransparent electrode 110 a and a p-side electrode 110 are formed on theexposed n-type cladding layer 106 and p-type contact layer 109.Moreover, the bottom side of the GaAs substrate 101 is polished ifnecessary.

The semiconductor white light emitting device of FIG. 1 is thusobtained.

In the above described method for manufacturing the semiconductor lightemitting device in this preferred embodiment, the light emitting layer102 is formed on the top of the GaAs substrate 101 suitable for theformation of the light emitting layer 102, and, this is bonded to thesemiconductor blue light emitting element 1. Therefore it is possible toprovide a semiconductor white light emitting device which has a smallnumber of crystal defects in the light emitting layer 102 and which hashigh reliability.

In the method for manufacturing the semiconductor light emitting elementin this preferred embodiment, the blue light emitting semiconductorlight emitting element 1 and the yellow light emitting semiconductorlaminate 2 are integrated with each other by bonding to fabricate asingle device. Therefore, the device can be used in a space smaller thanit is used to be in a case where two devices are used, and the number ofelectrodes can be reduced. In addition, since the device can be regardas a point light source by the integration, it is possible to provide anelement showing a small variation in emitting lights.

(Second Preferred Embodiment)

As can be seen from FIG. 4, one of different points of a semiconductorwhite light emitting device in the second preferred embodiment from thedevice in the first preferred embodiment (FIG. 1) is that the substrate104 side of a semiconductor light emitting element 1 serves as a lightemitting surface and that a semiconductor laminate 2 is bonded to theside of the light emitting surface.

FIG. 4 is a schematic sectional view showing the second preferredembodiment of a semiconductor white light emitting device according tothe present invention. The same reference numbers are given to elementscorresponding to those in the first preferred embodiment (FIG. 1). As inthe case with the first preferred embodiment (FIG. 1), a semiconductorlight emitting element 1 for emitting blue light E1 from an active layer107 by current injection and a semiconductor laminate 2 excited by theblue light E1 for emitting yellow light E2 from a light emitting layer102 are bonded to each other at a bonding surface A to constitute asemiconductor white light emitting device. As can be seen from FIG. 4,these light beams are emitted from the top side in the figure.

First, the semiconductor light emitting element 1 will be described. Oneof different points of the semiconductor light emitting element 1 fromthat in the first preferred embodiment (FIG. 1) is that the transparentelectrode 110 a is not used as a p-side electrode. In the semiconductorlight emitting element 1 of FIG. 4, a p-side electrode 110 of Ni/Au orthe like having a high reflectance is formed substantially on the entiresurface of a p-type contact layer 109. Thus, the blue light E1 emitteddownward from the active layer 107 in the figure can be reflected on thep-side electrode 110 to be effectively emitted from the light emittingsurface on the top side in the figure. Other principal features are thesame as those in the first preferred embodiment.

The semiconductor laminate 2 will be described below. One of differentpoints of the semiconductor laminate 2 from that in the first preferredembodiment (FIG. 1) is that the GaAs substrate 101 is removed and anSiO₂ protection layer 201 is formed on that surface. This is forpreventing light from being absorbed into the GaAs substrate 101. Thatis, in the device of FIG. 4, the semiconductor laminate 2 is bonded tothe light emitting surface. Accordingly if the GaAs substrate exists,the emitted blue light E1 and yellow light E2 are absorbed into the GaAssubstrate if the GaAs substrate exists. Therefore, the GaAs substrate isremoved to enhance the emission luminance.

A process for manufacturing the semiconductor light emitting element 1and the semiconductor laminate 2 is basically the same as that in thefirst preferred embodiment. Specifically, the InAlP/InGaAlP multilayerfilm 102 is formed so as to have a structure that 10 InAlP layers and 10In_(0.5)(Ga_(0.7)Al_(0.3))_(0.5)P layers are alternately stacked. TheGaAs substrate is removed with a hydrofluoric acid containing etchant.

The semiconductor white light emitting device of FIG. 4 thus obtainedwas mounted on a package so that the electrodes 110 and 111 faceddownward, and a current was injected. As a result, the blue light E1having a wavelength of 485 nm was emitted from the active layer 107, andthe yellow light E2 having a wavelength of 590 nm was emitted from thelight emitting layer 102 by exciting the blue light E1. These lightbeams passed through the oxide film 201 to be observed as white light.The color temperature of white light was about 8000 K, and the luminousintensity during the injection of a current of 20 mA was 3 cd in apackage having a radiation angle of 10 degrees.

Even if the light emitting surface is arranged on the side of thesubstrate 104 as in this preferred embodiment, it is possible todecrease the variation in tone in each device and the variation in tonedue to deterioration with age, as in the case with the first preferredembodiment.

(Third Preferred Embodiment)

As can be seen from FIG. 5, one of different points of a semiconductorwhite light emitting device in the third preferred embodiment from thedevice in the second preferred embodiment (FIG. 4) is that two lightemitting layers 302 and 304 are formed in a semiconductor laminate 2.

FIG. 5 is a schematic sectional view showing the third preferredembodiment of a semiconductor white light emitting device according tothe present invention. The same reference numbers are given to elementscorresponding to those in the second preferred embodiment (FIG. 4). Asemiconductor light emitting element 1 for emitting blue light E1 froman active layer 107 by current injection and a semiconductor laminate 2,which is excited by the blue light E1 for emitting green light E2 from afirst light emitting layer 304 and which is excited by the green lightE2 and the blue light E1 for emitting red light E3 from a second lightemitting layer 302, constitute a semiconductor white light emittingdevice. As can be seen from FIG. 5, these light beams are emitted fromthe top side in the figure.

First, the structure of the semiconductor light emitting element 1 isbasically the same as that in the second preferred embodiment (FIG. 4),so that the detailed description thereof is omitted.

The semiconductor laminate 2 will be described below. Between the firstlight emitting layer 304 and the second light emitting layer 302, afirst InAlP cladding layer 303 is provided. On the bottom face of thefirst light emitting layer 304 in the figure, a second InAlP claddinglayer 305 for bonding the semiconductor laminate 2 to the semiconductorlight emitting element 1 is formed. The top face of the second lightemitting layer 302 in the figure is covered with an oxide film 306 whichis a protection layer.

When a third InAlP cladding layer (not shown) is provided between theoxide film 306 and the second light emitting layer 302, it is possibleto adjust tone. That is, when the third InAlP cladding layer isprovided, carriers are effectively confined in the second light emittinglayer 302, so that the quantity of red light E3 increases, and the bluelight E1 is absorbed into the third InAlP cladding layer, so that thequantity of blue light E1 decreases.

As shown in FIG. 5, in the above described semiconductor light emittingelement 1 and semiconductor laminate 2, the side of the protection layer306 of the semiconductor laminate 2 serves as a light emitting surfaceto obtain white color due to the color mixture of three emissions E1, E2and E3. That is, the current is injected into the semiconductor lightemitting element 1 to obtain the blue light E1 emitted from the activelayer 107 having the MQW structure, and the first light emitting layer304 of the semiconductor laminate 2 is excited to obtain the green light2. Moreover, the second light emitting layer 302 is excited with theemitted blue light E1 and green light E2 to obtain the red light E3. Bythe hybridization of these light beams, white light is obtained.

Specifically, blue light E1 having a wavelength of 485 nm was emittedfrom the MQW layer 107, green light E2 having a wavelength of 565 nm wasemitted from the first light emitting layer 304, and red light E3 havinga wavelength of 620 nm was emitted from the second light emitting layer302, so that white light was observed by the color mixture. The colortemperature of white light was about 6500 K. The luminous intensityduring the injection of a current of 20 mA was 2 cd in a package havinga radiation angle of 10 degrees.

Even in the case of the semiconductor white light emitting device forobtaining white light by the color mixture of blue light E1, green lightE2 and red light E3, it is possible to reduce the variation in tone ineach device and the variation in tone due to deterioration with age, asin the case with the first preferred embodiment.

In the device of FIG. 5, the blue light E1 is emitted by the currentinjection, whereas the green light E2 and the red light E3 are emittedby optical pumping. Therefore, the variation in tone in each device dueto the lost balance of current injection doe not occur. For example, ina case where a current is injected into each of the blue light emittingactive layer, the green light emitting active layer and the red lightemitting active layer to obtain white light, when the quantity of thecurrent injected into the blue light emitting active layer increases dueto the lost balance of current injection, the tone is caused to near toblue. However, in the device of FIG. 5, such a variation in tone in eachdevice does not occur.

Referring to FIG. 6, a method for manufacturing the semiconductor whitelight emitting device of FIG. 5 will be described below. As shown inFIG. 6, one of the features of this manufacturing method is that a firstlight emitting layer 304 and a second light emitting layer 302 areformed on a GaAs substrate 301 suitable for the formation of the lightemitting layers 304 and 302, and thereafter, this is bonded to asemiconductor light emitting device 1.

FIG. 6 shows the structure of the semiconductor laminate 2 in the secondpreferred embodiment before the bonding. This will be specificallydescribed in accordance with manufacturing steps.

First, a GaAs substrate 301 is cleaned with an organic solvent and/or asulfuric acid containing etchant, and then, the substrate is introducedinto an MOCVD system. Then, the substrate is heated to 730° C., and anappropriate 5-Group material serving as a P material is supplied tosequentially crystal-grow a second light emitting layer 302 of anInAlP/InGaAlP multilayer film, a first InAlP cladding layer 303, a firstlight emitting layer 304 of an InAlP/InGaAlP multilayer film, and asecond InAlP cladding layer 305 to further grow a GaAs cap layer 307 onthe surface thereof to obtain a stacked structure shown in FIG. 6. TheGaAs cap layer 307 is a protection layer which is ultimately removed.

The thickness of these crystalline layers are shown in Table 3.

TABLE 3 InAlP/InGaAlP Light Emitting Layer 302  30 nm/50 nm InAlPCladding Layer 303 500 nm or less InAlP/InGaAlP Light Emitting Layer 304 30 nm/50 nm InAlP Cladding Layer 305 300 nm or less GaAs Cap Layer 307100 nm

Specifically, the second light emitting layer 302 has a structurewherein 20 InAlP layers having a thickness of 30 nm and 20In_(0.5)(Ga_(0.8)Al_(0.2))_(0.5)P layers having a thickness of 50 nm arealternately stacked. The first light emitting layer 304 has a structurewherein 20 InAlP layers having a thickness of 30 nm and 20In_(0.5)(Ga_(0.6)Al_(0.4))_(0.5)P layers having a thickness of 50 nm arealternately stacked. The InAlP contact layer 305 serves both as anadhesive layer for bonding the semiconductor laminate 2 to thesemiconductor light emitting element 1 and as a protection layer forprotecting the light emitting layer 304, and at the same time, also havethe function of confining light in the light emitting layer 304.

Then, the cap layer 307 of the semiconductor laminate 2 thusmanufactured is removed, and the semiconductor laminate 2 is bonded tothe semiconductor light emitting element 1 as in the case with the firstpreferred embodiment. Then, the GaAs substrate 301 is etched to beremoved, and a protection layer 306 is formed on the surface thusetched, so that the device structure of FIG. 5 is obtained.

In the above described method for manufacturing the semiconductor lightemitting device of FIG. 5, as in the case with the first preferredembodiment, the light emitting layers 302 and 304 are formed on the topof the GaAs substrate 301 suitable for the formation of the lightemitting layers 302 and 304, and thereafter, this is bonded to thesemiconductor blue light emitting element 1, so that it is possible toprovide a semiconductor white light emitting device which has a smallnumber of crystal defects in the light emitting layers 302 and 304 andwhich thus has high reliability.

In the method for manufacturing the device wherein the semiconductorlaminate 2 is provided on the side of the light emitting surface, asshown in FIG. 5, it is possible to prevent light from being absorbedinto the GaAs substrate 301 by etching and removing the GaAs substrate301, so that it is possible to enhance the emission luminance of thedevice.

In the method for manufacturing the semiconductor light emitting deviceof FIG. 5, the semiconductor light emitting element 1 for emitting bluelight E1 and the semiconductor laminate 2 for emitting green light E2and red light E3 are integrated with each other by bonding to fabricatea single device. Therefore, the device can be used in a smaller spacethan that in a case where two or three devices are used, and the numberof electrodes can be reduced. In addition, since the device can beregarded as a point light source by the integration, it is possible toprovide a device having a small variation in emission.

(Fourth Preferred Embodiment)

As can be seen from FIG. 7, one of different points of a semiconductorwhite light emitting device in the fourth preferred embodiment from thedevice in the first preferred embodiment (FIG. 1) is that an n-typesemiconductor substrate 404 such as an n-type GaN, n-type SiC, n-type Sisubstrate is used as the substrate of a semiconductor light emittingelement 1, and that an n-type electrode 111 is formed on the reversesurface of the substrate 101 n of a semiconductor laminate 2. In thedevice of FIG. 7, a current is injected from the n-side electrode 111into an active layer 107 via an n-type GaAs substrate 101 n, a lightemitting layer 102 n of an n-type InAlP/InGaAlP multilayer film, ann-type InAlP cladding layer 103 n, an n-type semiconductor substrate404, an n-type AlGaN buffer layer 105 n and a GaN contact layer 106.Other principal structures are the same as those in the first preferredembodiment.

Even in the case of the semiconductor light emitting device wherein theelectrodes are provided on the top and bottom as shown in FIG. 7, it ispossible to reduce the variation in tone in each device and thevariation in tone due to deterioration with age, as in the case with thefirst preferred embodiment.

Even in the case of the device of FIG. 7, it is possible to use amanufacturing method which is substantially the same as that in thefirst preferred embodiment (FIG. 1), and it is possible to obtain adevice having high reliability, as in the case with the first preferredembodiment. Moreover, in the case of the device of FIG. 7, an etchingstep of forming an n-side electrode is not required to carry out, sothat the manufacturing method is simplified.

(Fifth Preferred Embodiment)

As can be seen from FIG. 8, one of different points of a semiconductorwhite light emitting device in the fifth preferred embodiment from thedevice in the first preferred embodiment (FIG. 1) is that thenon-transparent GaAs substrate 101 of a semiconductor laminate 2 isetched to be removed and that another transparent substrate 501 isbonded to a bonding surface A2. Specifically, a GaP substrate or ZnSesubstrate for transmitting yellow light is used as the transparentsubstrate 501. Other principal structures are the same as those in thefirst preferred embodiment. Furthermore, the bonding surface A in thefirst preferred embodiment (FIG. 1) corresponds to the bonding surfaceAl in the fifth preferred embodiment (FIG. 8).

In the device of FIG. 8, yellow light E2 s emitted from an InAlP/InGaAlPlight emitting layer 102 can also be emitted from the side of the newlybonded substrate 501 as shown by a broken line. Therefore, if, forexample, when the inner wall surface of a package is formed as arecessed surface to emit the radiation E2 s upward, the radiation E2 scan be effectively utilized.

In the above described first through fifth preferred embodiments, anInAlP layer 103 was used as a cladding layer (also serving as a contactlayer) for bonding the light emitting layer 102 of a semiconductorlaminate 2 to a semiconductor light emitting element 1. On the top ofthe InAlP cladding layer 103, a cladding layer of another material maybe formed in place of the cladding layer 103. Such a cladding layer maybe made of, e.g., GaN or GaP. By providing such a cladding layer, thelight confining effect in a multilayer film 102 can be enhanced. A GaNcladding layer is particularly preferable since it transmits blue light,though it is a polycrystalline thin film. In accordance with thematerial of a substrate to be bonded, GaAlAs or InGaAlP may be used.

Although etching and/or polishing was used as a pre-treatment beforebonding, gas etching or thermal cleaning in various amorphous gases maybe carried out. Moreover, the annealing atmosphere and temperature canbe suitably changed. When a high annealing temperature is used, anatmosphere gas may be selected to apply a suitable pressure in order toprevent atoms from being emitted and removed from crystal.

For bonding, an adhesive may be used. For example, if an adhesive isused in the device in the fifth preferred embodiment (FIG. 5), settingthe refractive index of the adhesive to be at a value between therefractive index of the sapphire substrate 104 and the refractive indexof the InAlP cladding layer, enables the reduction in quantities of bluelight E1 and yellow light E2 reflected on the bonding surface Al, sothat it is possible to enhance the emission luminance of the device.

(Sixth Preferred Embodiment)

FIG. 9 is a schematic sectional view of the sixth preferred embodimentof a semiconductor white light emitting device according to the presentinvention. Unlike the preceding preferred embodiments wherein thesemiconductor light emitting device is bonded to the semiconductorlaminate, a light emitting layer 702 and an active layer 706 in thispreferred embodiment, are formed on an n-type GaAs substrate 701 bycrystal growth. That is, on the n-type GaAs substrate 701, there aresequentially stacked an n-type InAlP/InGaAlP light emitting layer 702for emitting yellow light E2 by optical pumping, an n-type ZnSe bufferlayer 703, an n-type ZnMgSSe cladding layer 704, an n-type ZnSe opticalguiding layer 705, a ZnSe/ZnCdSe MQW active layer 706 for emitting bluelight E1 by current injection, a p-type ZnSe optical guiding layer 707,a p-type ZnMgSSe cladding layer 708, and a p-type ZnTe/ZnSe superlatticecontact layer 709. On the p-type contact layer 709, a p-side transparentelectrode 710 a and a p-side electrode 710 are formed, and on the n-typeGaAs substrate 701, an n-side electrode 711 is formed.

For the crystal growth of the device of FIG. 9, the MOCVD method and theMBE method are combined. That is, the MOCVD method is used for thecrystal growth of the n-type InAlP/InGaAlP light emitting layer 702 onthe n-type GaAs substrate 701, and the MBE method was used for thegrowth of the n-type ZnSe buffer layer 703 to the p-type ZnTe/ZnSesuperlattice contact layer 709 thereon. This is because a goodconductive type control can be achieved by using the MBE methodparticularly for ZnSe compound p-type conductive layers.

In the semiconductor white light emitting device thus formed, blue lightE1 is emitted from the active layer 706 by passing a current between theelectrodes 710 and 711. A part of the blue light E1 passes through theelement to be absorbed into the light emitting layer 702 to exciteyellow light E2. This yellow light E2 is emitted from the top side inthe figure. By the hybridization of the blue light E1 and yellow lightE2, white light is obtained.

In fact, white light was observed by the color mixture of blue light E1having a wavelength of 485 nm and yellow light E2 having a wavelength of590 nm. The color temperature of the white light was about 8000 K, andthe luminous intensity during the injection of a current of 20 mA was 2cd in a package having a radiation angle of 10 degrees.

Even in the case of the above described semiconductor light emittingdevice of FIG. 9 using the ZnSe compound semiconductor light emittingelement 1, it is possible to reduce the variation in tone in each deviceand the variation in tone due to deterioration with age, as in the casewith the first preferred embodiment.

A method for manufacturing the device of FIG. 9 will be brieflydescribed below. First, an n-type GaAs substrate 701 is cleaned with anorganic solvent and/or a sulfuric acid containing etchant, and then, thesubstrate is introduced into an MOCVD system. Then, the substrate isheated to 730° C., and an appropriate 5-Group material serving as a Pmaterial is supplied to grow an n-type InAlP/InGaAlP light emittinglayer 702. Then, the substrate is transferred to an MBE system to growthereon an n-type ZnSe buffer layer 703 to a p-type ZnTe/ZnSesuperlattice contact layer 709. Specifically, the n-type InAlP/InGaAlPlight emitting layer 702 was formed so as to have a structure wherein 20InAlP layers and 20 In_(0.5)(Ga_(0.7)Al_(0.3))_(0.5)P layers arealternately stacked.

As described above, in the semiconductor light emitting device of FIG.9, the n-type InAlP/InGaAlP light emitting layer 702 and the ZnSe/ZnCdSeMQW active layer 706 are formed on the n-type GaAs substrate 701 bycrystal growth, so that it is possible to simplify the manufacturingprocess.

In addition, since the lattice constant of the ZnSe compoundsemiconductor is close to the lattice constant of the GaAs compoundsemiconductor, even if the above described crystal growth is carriedout, it is possible to provid a semiconductor white light emittingdevice which has a small number of crystal defects and which has highreliability.

(Seventh Preferred Embodiment)

As can be seen from FIG. 10, one of different points of a semiconductorwhite light emitting device in the seventh preferred embodiment from thedevice in the sixth preferred embodiment (FIG. 9) is that etching iscarried out from the side of a p-type contact layer 709 to expose ann-type buffer layer 703 and that arm-side electrode 711 is formed on then-type buffer layer 703. Other principal constructions are the same asthose in the sixth preferred embodiment.

Even in the case of the device of FIG. 10, it is possible to obtainwhite light by color mixture as in the case with the sixth preferredembodiment, so that it is possible to obtain the same advantages asthose in the sixth preferred embodiment.

While the InGaAlP materials semiconductors and the ZnSe compoundsemiconductors have been crystal-grown by the MOCVD method and the MBEmethod, respectively, in the sixth and seventh preferred embodiments,both may be crystal-grown by the MBE method. Also in the case of thematerial system in the sixth and seventh preferred embodiments, twolight emitting layers may be formed on separate element substrates,respectively, to bond and integrate the substrates with each other as inthe case with the first preferred embodiment.

(Eighth Preferred Embodiment)

In the following eighth through eleventh preferred embodiments, therewill be described a device wherein a semiconductor laminate 2 having adouble-hetero structure is bonded to a part of a light emitting surfaceof a GaN compound semiconductor light emitting element 1 or a part ofthe opposite surface thereto, as shown in, e.g., FIG. 11. Furthermore,in the following preferred embodiments, the detailed description of themanufacturing process is omitted.

FIG. 11 is a schematic sectional view showing the eighth preferredembodiment of a semiconductor white light emitting device according tothe present invention. The same reference numbers are given to elementscorresponding to those in the first preferred embodiment (FIG. 1). Asemiconductor white light emitting device comprises a semiconductorlight emitting element 1 for emitting blue light E1 by currentinjection, and a semiconductor laminate 2 excited by the blue light E1for emitting yellow light E2. As can be seen from FIG. 12, these lightbeams are emitted from the top side in the figure.

First, the semiconductor light emitting element 1 will be described. Onthe bottom face of a sapphire substrate 104 in the figure, there aresequentially formed a buffer layer 105, an n-type GaN cladding layer106, an InGaAlN active layer 107 a, a p-type AlGaN cladding layer 108and a p-type GaN contact layer 109. Although the thickness of each ofthe layers 104 to 109 is several μm and the thickness of the sapphiresubstrate 104 is hundreds μm, the scale factor thereof is changed inFIG. 11 for the purpose of easier explanation of the stacked layers 104through 109.

The wavelength of light emitted from the above described InGaAlN activelayer 107 is designed to emit blue light E1 by controlling thecomposition ratio of In and Al of the active layer. The compositionratio of Al may be 0 so that the active layer is made of InGaN. If thisactive layer 107 a has a single-quantum well or multi-quantum wellstructure of a thin film having a thickness of about 1 nm to 10 nm, itis possible to realize high luminance. A current is injected into theactive layer 107 a from an n-side electrode 111, which is formed on then-type cladding layer 106, and from a p-side electrode 110 which isformed on the p-type contact layer 109. The p-side electrode 110 and then-side electrode 111 are preferably made of Ni/Au and Ti/Al,respectively, which are materials having a high reflectance forreflecting blue light emitted from the active layer 107 a. Thus, theblue light E1 emitted from the active layer 107 a downward in the figurecan be reflected on the p-side electrode 110 and the n-side electrode111 to be emitted from the light emitting surface on the top side in thefigure. Furthermore, the portions shown by slant lines in the figure,such as the p-side electrode 110 and the n-side electrode 111, are theportions having the property of reflecting the blue light E1 and theyellow light E2.

The semiconductor laminate 2 will be described below. The semiconductorlaminate 2 has a structure wherein an InGaAlP light emitting layer 102 cis located between a p-type InGaAlP cladding layer 102 b and an n-typeInGaAlP cladding layer 102 a. The light emitting layer 102 c is designedto emit the yellow light E2 by controlling the composition ratio of3-Group elements, In, Ga and Al, of InGaAlP. The thickness of the lightemitting layer 102 is preferably in the range of from 1 nm to 10 μm.That is, when the light emitting layer 102 c has a single-quantum wellor multi-quantum well structure of a thin film having a thickness of onenm to tens nm, the luminous efficiency of yellow light increases toincrease the intensity of yellow light, and when the light emittinglayer 102 c is made of a single layer or multilayer film having athickness of tens nm to 10 μm, the absorption efficiency of blue lightincreases to increase the intensity of yellow light. The two claddinglayers 102 a and 102 b on both sides of the light emitting layer 102 chave a greater band gap than the light emitting layer 102 c. That is,the semiconductor laminate 2 has a double-hetero structure. Because ofthe double-hetero structure, electrons and holes generated by the bluelight E1 emitted from the semiconductor light emitting element 1 can beeffectively confined in the light emitting layer 102 c, so that theluminous efficiency of the yellow light E2 can increase to increase theemission luminance of the yellow light E2. Also, because of thedouble-hetero structure, the emission luminance of the yellow light E2increases even if the light emitting layer 102 c is made of a singlelayer film. If the cladding layers for locating the light emitting layer102 c are p-type and n-type cladding layers as in this preferredembodiment, the intensity of the yellow light E2 of the light emittinglayer 102 c further increases. This results was obtained by theinventors' experiment. It is analyzed that the reason for this is thatthe absorption efficiency is increased by the internal field. No elementmay be doped into the cladding layers 102 a and 102 b. In the case ofsuch undoping, the crystalline characteristics of the light emittinglayer 102 c are improved, i.e., the non-emission center of the lightemitting layer 102 decreases, and the intensity of the yellow light E2in the light emitting layer 102 c increases.

When the semiconductor laminate 2 having the double-hetero structure isused as in the device of FIG. 11, the area of the semiconductor laminate2 is preferably set to be ⅓ to ⅔ of the area of the sapphire substrate104 on the top side in the figure. That is, as described above, when thesemiconductor laminate 2 has the double-hetero structure, the intensityof the yellow light E2 increases. However, if the double-heterostructure is used, the n-type cladding layer 102 a absorbs the bluelight E1, so that the intensity of the blue light E1 decreases.Therefore, when the semiconductor laminate 2 is the double-heterostructure and when the area of the semiconductor laminate 2 has the sameas that on the top side in the figure, the intensity of the yellow lightE2 is too strong, so that the tone of white light is caused to approachyellow. Therefore, if the area of the semiconductor laminate 2 is set tobe ⅓ to ⅔ of the area of the sapphire substrate, it is possible toobtain white light having a good balance.

The thickness of the above described p-type cladding layer 102 b ispreferably 300 nm or less, and more preferably 100 nm or less. Thereason for this is that the quantity of blue light El for exciting thelight emitting layer 102 c decreases when the p-type cladding layer 102b is too thick since the p-type cladding layer 102 b has the property ofabsorbing blue light E1. On the other hand, since the n-type claddinglayer 102 a has the property of transmitting yellow light E2, itsthickness may be increased if necessary.

As shown in FIG. 11, the semiconductor laminate 2 is bonded to a part ofthe top side of the sapphire substrate 104 of the semiconductor lightemitting element 1 in the figure. For example, this semiconductorlaminate 2 may be formed by sequentially forming the n-type claddinglayer 102 a, the light emitting layer 102 c and the p-type claddinglayer 102 b on the GaAs substrate, heat-treating the substrate at atemperature of 460° C. to 750° C. in an atmosphere of an inert gas,bonding the p-type cladding layer 102 b on the top side of the sapphiresubstrate 104 in the figure, and etching and removing the GaAssubstrate.

In the above described semiconductor light emitting element 1 andsemiconductor laminate 2, blue light E1 is emitted from the active layer104 of the semiconductor light emitting element 1, and a part of theblue light E1 is incident on the semiconductor laminate 2. The incidentblue light E1 excites the light emitting layer 102 c of thesemiconductor laminate 2, so that yellow light E2 is emitted from thelight emitting layer 102. Thus, the blue light E1 emitted from theactive layer 107 and the yellow light E2 emitted from the light emittinglayer 102 c are mixed to realize white light.

Referring to the chromaticity diagram of FIG. 12, this white light willbe described below in detail. FIG. 12 is an xy chromaticity diagramdefined by International Commission on Illumination (CIE). The emissionwavelength of an InGaAlN active layer, such as the active layer 107 a ofthe semiconductor light emitting element 1 of FIG. 11, can be in therange of from 380 nm to 500 nm as shown on the left side of FIG. 12. Theemission wavelength of an InGaAlP light emitting layer, such as thelight emitting layer 102 c of the semiconductor laminate 2, can be inthe range of from 540 nm to 750 nm as shown on the right side of FIG.12. If for example, the color mixture of blue light having a wavelengthof 476 nm emitted from the InGaAlN active layer with yellow light havinga wavelength of 578 nm emitted from the InGaAlP light emitting layer isintended to be carried out, a straight line drawn between a white circleof 476 in the lower-left blue region and a white circle of 578 in theupper-right yellow region is considered. Then, it can be seen that thisstraight line passes through a white region. It can thus be seen fromFIG. 12 that white light can be realized by the color mixture of theblue light emitted from the semiconductor light emitting element 1 andthe yellow light E2 emitted from the semiconductor laminate 2.

Similarly, it can be seen from FIG. 12 that white light can be realizedby the color mixture of bluish green light with red light when theemission wavelength of the InGaAlN active layer 107 a is set to be 495nm and the emission wavelength of the InGaAlP light emitting layer 102 cis set to be 750 nm.

In the above described semiconductor of FIG. 11, it is possible todecrease the variation in tone in each device. This is because unlikefluorescent material, the thickness, composition, and othercharacteristics and area of the semiconductor laminate 2 hardly vary ineach element. That is, by using a standardized mass production processgenerally used for the manufacturing of semiconductor elements, thesemiconductor laminate 2 can be manufactured with high repeatability sothat the thickness, composition and other characteristics hardly vary,and can be easily worked so as to have the same area. Then, when thethickness, composition, and other characteristics and area of thesemiconductor laminate 2 are uniform for each element, the ratio of theblue light E1 emitted from the semiconductor light emitting element 1 tothe yellow light E2 emitted from the semiconductor laminate 2 does notvary for each element, so that the tone does not vary for each element.

In the semiconductor light emitting device of FIG. 11, the tone can alsobe adjusted by changing the area of the semiconductor laminate 2.Because of this, when the luminous efficiency of the semiconductorlaminate 2 varies for some reason or other, for example, the tone can beadjusted. In a simple manner, the luminous efficiency of thesemiconductor laminate 2 decreases, the area of the semiconductorlaminate may be increased.

Also, it is necessary to change the tone of white light is intended, thetone can be easily changed by changing the area of the semiconductorlaminate 2 as described above. For example, when an element for emittingwhite light having a tone close to blue is intended to be manufacturedas a displaying element, the area of the semiconductor laminate 2 foremitting yellow light may be decreased.

Moreover, in the semiconductor light emitting device of FIG. 11, it ispossible to further improve the emission luminance than that inconventional elements. That is, since the semiconductor laminate 2 isformed only on a part of the light emitting surface in the element ofFIG. 11, it is possible to utilize blue light which does not passthrough the semiconductor laminate 2 serving as a wavelength convertingregion, i.e., blue light having a high luminance directly emitted fromthe semiconductor light emitting element 1, so that it is possible toimprove the emission luminance.

(Ninth Preferred Embodiment)

As can be seen from FIG. 13, one of different points of the ninthpreferred embodiment from the eighth preferred embodiment is that alight emitting surface is arranged on the side of a p-type contact layer109.

FIG. 13 is a schematic sectional view of the ninth preferred embodimentof a semiconductor white light emitting device according to the presentinvention. As in the case with the eighth preferred embodiment (FIG.11), a semiconductor white light emitting device comprises asemiconductor light-emitting element 1 for emitting blue light E1 froman active layer 107 by current injection, and a semiconductor laminate 2excited by the blue light E1 for emitting yellow light E2 from a lightemitting layer 102. These light beams are emitted from the lightemitting surface on the top side in the figure.

First, the structure of the semiconductor light emitting element 1 isbasically the same as that in the first preferred embodiment (FIG. 1),so that the detailed description thereof is omitted.

The semiconductor laminate 2 will be described below. The semiconductorlaminate 2 has a structure wherein a light emitting layer 102 of anInAlP/InGaAlP multilayer film is located between a p-type InGaAlPcladding layer 102 b and an n-type InGaAlP cladding layer 102 a. On thebottom side of the n-type cladding layer 102 a, a reflecting film 120for reflecting yellow light emitted from the light emitting layer 102 isformed. This reflecting film may be made of a metal film of Al, Ag, Auor Cu or an alloy thereof, and have a thickness of 0.1 μm to 10 μm.Thus, the yellow light E2 emitted from the light emitting layer 102downward in the figure can be reflected on the reflecting film 120 to beemitted from the light emitting surface. The semiconductor laminate 2thus manufactured is bonded to a part of the bottom face (second face)in the figure of the sapphire substrate 104 of the semiconductor lightemitting element 1.

Even if the light emitting surface is arranged on the side of the p-typecontact layer 109 as in this preferred embodiment, the same advantagesas those in the eighth preferred embodiment can be obtained.

(Tenth Preferred Embodiment)

As can be seen from FIG. 14, one of different points of the tenthpreferred embodiment from the ninth preferred embodiment is that asemiconductor laminate 2 is formed on the side of a light emittingsurface on the top side in the figure.

FIG. 14 is a schematic sectional view of the tenth preferred embodimentof a semiconductor white light emitting device according to the presentinvention. As in the case with the ninth preferred embodiment (FIG. 13),a semiconductor white light emitting device comprises a semiconductorlight emitting element 1 for emitting blue light E1 from an active layer107 by current injection, and a semiconductor laminate 2 excited by theblue light E1 for emitting yellow light E2 from a light emitting layer102. As can be seen from FIG. 14, the light emitted from this device isemitted from the light emitting surface on the top side in the figure.

First, the semiconductor light emitting element 1 will be described. Oneof different points of the semiconductor light emitting element 1 fromthat in the ninth preferred embodiment (FIG. 13) is that a reflectinglayer 120 for reflecting blue light El emitted from an active layer 107and yellow light E2 emitted from a light emitting layer 102 is formed onthe bottom side of a sapphire substrate 104. This reflecting film may bemade of a metal film of Al, Ag, Au or Cu or an alloy thereof, and have athickness of 0.1 μm to 10 μm. Thus, the blue light E1 emitted from theactive layer 107 downward in the figure and the yellow light E2 emittedfrom the light emitting layer 102 downward in the figure can bereflected on the reflecting film 120 to be emitted from the lightemitting surface on the top side in the figure. Other principalstructures are the same as those in the ninth preferred embodiment (FIG.9).

The semiconductor laminate 2 will be described below. As in the casewith the ninth preferred embodiment, the semiconductor laminate 2 has astructure wherein the light emitting layer 102 of an InAlP/InGaAlPmultilayer film is located between a p-type InGaAlP cladding layer 102 band an n-type InGaAlP cladding layer 102 a. This semiconductor laminate2 is bonded to the top of a p-side transparent electrode 110 a of thesemiconductor light emitting element 1. As in the case with the eighthpreferred embodiment, a heat treatment is carried out in an atmosphereof an inert gas during bonding. However, as a result of the inventors'experiment, the bonding temperature for the semiconductor laminate 2 maybe in the range of from 150° C. to 450° C. although the bondingtemperature in the eighth embodiment is in the range of from 460° C. to750° C. That is, as a result of the inventors' experiment, it was foundthat if the semiconductor laminate 2 was bonded to the top of thetransparent electrode 109, it is possible to bond it at a lowertemperature than the case where it was bonded to the sapphire substrate104, with the same bonding strength.

Even if the semiconductor laminate 2 is formed on the top of thetransparent electrode 110 a on the side of the light emitting surface asin the semiconductor light emitting device in this preferred embodiment,the same advantages as those in the ninth and eighth preferredembodiments can be obtained.

Since the semiconductor laminate 2 is bonded to the transparentelectrode 110 a in the semiconductor light emitting element in thispreferred embodiment, it is possible to utilize reflection on thetransparent electrode 110 a, so that it is possible to more effectivelyextract yellow light emitted from the light emitting layer 102.

(Eleventh Preferred Embodiment)

As can be seen from FIG. 15, one of different points of the eleventhpreferred embodiment from the eighth preferred embodiment (FIG. 11) isthat an n-side electrode 111 is provided on the top of a substrate 404 nusing an n-type GaN substrate 404 n and that a low-pass filter 130 isprovided in a semiconductor laminate 2.

FIG. 15 is a schematic sectional view of the eleventh preferredembodiment of a semiconductor white light emitting device according tothe present invention. Just like the eight preferred embodiment (FIG.11), a semiconductor white light emitting device comprises thesemiconductor light emitting element 1 for emitting blue light E1 froman active layer 107 by current injection, and a semiconductor laminate 2excited by the blue light E1 for emitting yellow light E2 from a lightemitting layer 102. The light emitted from this device is emitted fromthe light emitting surface on the top side in the figure.

First, the semiconductor light emitting element 1 will be described. Onthe bottom face of an n-type GaN substrate 404 n in the figure, thereare sequentially formed an n-type AlGaN buffer layer 105 n, an n-typeGaN cladding layer 106, an active layer 107 having a GaN/InGaNmulti-quantum well structure, a p-type AlGaN cladding layer 108 and ap-type GaN contact layer 109. A current is injected into the activelayer 107 from an n-side electrode 111 of Ti/Al or the like formed onthe n-type GaN substrate 404 n and from a p-type electrode 110 of Ni/Auor the like formed on the p-type contact layer 109. As described above,the buffer layer 105 n is made of an n-type AlGaN since the current isinjected into the active layer 107 via the buffer layer 105 n from then-side electrode 110 provided on the substrate 404 n in the element ofFIG. 15.

The semiconductor laminate 2 will be described below. The semiconductorlaminate 2 has a structure wherein the light emitting layer 102 of anInAlP/InGaAlP multilayer film is located between a p-type InGaAlPcladding layer 102 b and an n-type InGaAlP cladding layer 102 a. Inaddition, in the device of FIG. 15, the semiconductor laminate 2 isprovided with the low-pass filter 130. As shown in FIG. 16, the low-passfilter 130 has a high reflectance with respect to the yellow light E2emitted from the light emitting layer 102, and a low reflectance withrespect to the blue light E1 emitted from the active layer 107. That is,the low-pass filter 130 has the property of reflecting the yellow lightE2 emitted from the light emitting layer 102 and transmitting the bluelight E1 emitted from the active layer 107. As in the case with theeighth preferred embodiment (FIG. 11), the semiconductor laminate 2 isbonded on the top side (the side of the second surface) of the substrate404 n of the semiconductor light emitting element 1 in the figure.

When the n-type GaN substrate 404 n is used as a substrate as in theelement in this preferred embodiment, the distortion due to the latticeunconformity between the substrate 404 n and the crystal growth layers105 n through 109 including the active layer 107 is decreased, so thatit is possible to realize a light emitting device having highreliability.

When the low-pass filter 130 is provided as in the device in thispreferred embodiment, it is possible to efficiently extract yellow lightemitted from the light emitting layer 107, so that it is possible tofurther enhance luminance.

While the n-type GaN substrate 404 n has been used as the substrate inthe above described eleventh preferred embodiment, an n-type SiCsubstrate may be used as in the fourth preferred embodiment. When then-type SiC substrate is used, it is possible to realize a device whichhas good radiation characteristics and which does not decrease luminanceeven at a high temperature of higher than 80° C.

(Twelfth Preferred Embodiment)

In the following twelfth and thirteenth preferred embodiments, therewill be described other semiconductor white light emitting devices whichare relevant to the present invention and wherein the variation in tonein each device is small.

As shown in FIG. 17, the twelfth preferred embodiment is characterizedin that an ion implantation region 809 is provided in a part of anactive layer 107.

FIG. 17 is a schematic sectional view showing the twelfth preferredembodiment of a semiconductor white light emitting device according tothe present invention. On the bottom face of a sapphire substrate 104 inthe figure, there are sequentially formed a buffer layer 105, an n-typeGaN cladding layer 106, an active layer 107 having a GaN/InGaNmulti-quantum well structure, a p-type AlGaN cladding layer 108 and ap-type GaN contact layer 109.

One of the features of this preferred embodiment is that the ionimplantation region 809 is provided to form an ion implanted region in apart of the active layer 107. Ions in the ion implantation region 809form the emission center in the active layer 107 to absorb blue light E1to emit yellow light E2. The device of FIG. 17 realizes white light bythe blue light E1 emitted from the active layer 107 and the yellow lightE2 emitted from the ion implantation region 809. These light beams areemitted from the light emitting surface on the top side in the figure.

A current is injected into the above described active layer 107 from then-side electrode 111 formed on the n-type cladding layer 106 and fromthe p-side electrode 110 formed on the p-type contact layer 109. Thep-side electrode 110 and the n-side electrode 111 are preferably made ofAu/Ni and Ti/Al, respectively, which are material having a highreflectance for reflecting blue light and yellow light. Because of thisconstitution, the blue light E1 emitted downward from the active layer107 and the yellow light E2 emitted downward from the ion implantationregion 809 can be reflected on the p-side electrode 110 and the n-sideelectrode 111 to be emitted from the light emitting surface on the topside in the figure.

The semiconductor light emitting device of FIG. 17 can decrease thevariation in tone in each device. This is because the ion concentrationand implantation region in the ion implantation region 809 hardly varyin each device. That is, since the ion implantation can be carried outwith high repeatability by a standardized process generally used in themanufacturing of semiconductor device, the ion concentration andimplantation region in the ion implantation region 809 is uniform ineach device. Thus, the ratio of the quantity of the blue light Elemitted from the active layer 107 to the quantity of the yellow light E2emitted from the ion implantation region 809 does not vary everyelement. Therefore, the tone does not vary device by device.

In the device of FIG. 17, even if the luminous efficiency of the activelayer 809 varies for some reason or other, the ratio of the quantity ofthe blue light E1 to the quantity of the yellow light E2 is the same, sothat the tone does not vary. For example, even if the luminousefficiency of the active layer 107 decreases for some reason or other,both of the blue light E1 and the yellow light E2 are weaken at the samerate, and the ratio of the quantity of the blue light E1 to the quantityof the yellow light E2 is the same, so that the tone does not vary.Thus, the variation in tone in each device is very small in the deviceof FIG. 17.

In the semiconductor light emitting device of FIG. 17, it is possible toeasily adjust the tone by changing the area of the ion implantationregion 809. By doing so, it is possible to easily vary the tone of whitelight if necessary. For example, when a device for emitting white lighthaving a tone close to blue is intended to be manufactured as adisplaying device, the area of the ion implantation region 809 may bedecreased.

Moreover, in the semiconductor light emitting device of FIG. 17, theemission luminance can be made higher than that in conventionalelements. That is, light emitted directly from the semiconductor lightemitting element 1 can be utilized to increase the emission luminance.

(Thirteenth Preferred Embodiment)

As shown in FIG. 18, the thirteenth preferred embodiment ischaracterized in that fluorescent material 903 for emitting yellow lightE2 are formed in part of a reflector 902.

FIG. 18 is a schematic sectional view showing the thirteenth preferredembodiment of a semiconductor white light emitting device according tothe present invention. The semiconductor light emitting device comprisesa semiconductor light emitting element 1 for emitting blue light E1,emitted from the semiconductor light emitting element 1, and afluorescent material 903 applied on several parts of the reflectingsurface of the reflector 902 for converting the wavelength of the bluelight E1 to emit yellow light E2. The semiconductor light emittingelement 1 and the reflector 902 are integrally formed via a mold resin904. The semiconductor light emitting element in the ninth preferredembodiment (FIG. 13) may be used as the semiconductor light emittingelement 1 in this embodiment. The fluorescent material 903 may be formedof, e.g., YAG: Ce. The fluorescent material 903 is thinly applied on theseveral parts of the reflecting surface of the reflector 902 so as tohave a small thickness.

The device of FIG. 18 realizes white light by the blue light E1reflected on the reflector 902 and the yellow light E2 emitted on thefluorescent material 903.

The semiconductor light emitting device of FIG. 18 can decrease thevariation in tone in each device. The reason for this is as follows.

First, the area of fluorescent material regions, on which thefluorescent material 903 is applied, hardly varies in each device. Thatis, since the surface of the reflector 902 is even, it is possible toeasily adjust the area thereof, so that the area of the fluorescentmaterial regions hardly varies in each device.

Secondly, when the volume of a fluorescent material region varies whilemaintaining the area thereof on which the fluorescent material isapplied, the variation in tone in each device is small. That is, in theapplied fluorescent material 903 in the fluorescent material region, aportion near the semiconductor light emitting element 900, i.e., aportion near the surface of the fluorescent material region, has a highconversion efficiency for converting the blue light E1 into the yellowlight E2, and even if the thickness of the fluorescent material regionvaries, the quantity of the fluorescent material 903 arranged near thesurface of the fluorescent material region and having a high conversionefficiency does not vary, and it is only the quantity of the fluorescentmaterial 903 having a low conversion efficiency that varies. Thus, evenif the thickness of the fluorescent material region varies, the quantityof the fluorescent material 903 having a high conversion efficiency andhaving a great influence on the intensity of the yellow light E2 hardlyvaries. Therefore, even if the thickness of the fluorescent materialregion varies, this variation has a little influence on the intensity ofthe yellow light E2, so that the variation in tone in each device issmall.

Thus, the semiconductor light emitting device of FIG. 18 can decreasethe variation in tone in each device.

The semiconductor light emitting device of FIG. 18 can easily adjust thetone by changing the area of the fluorescent material regions on whichthe fluorescent materials 903 is applied. Thus, for example, even if theconversion efficiency of the fluorescent material 903 varies, it ispossible to adjust the tone easily. For example, when the conversionefficiency of the fluorescent material 903 decreases, the tone may beadjusted by increasing the area of the fluorescent material regions.

In addition, the semiconductor light emitting device of FIG. 18 canadjust the tone by changing the area of the fluorescent material regionon which the fluorescent material 903 is applied. Thus, it is possibleto easily change the tone of white light if necessary. For example, whena device for emitting white light having a tone close to blue isintended to be manufactured, the area of the fluorescent materialregions may be decreased.

Since the fluorescent material is applied on the reflector in thesemiconductor light emitting device of FIG. 18, it is possible to easilyadjust the angle of visibility.

Moreover, the semiconductor light emitting device of FIG. 18 can furtherimprove the emission luminance than conventional devices. That is, inthe device of FIG. 18, it is possible to utilize light emitted directlyfrom the semiconductor light emitting device, and it is possible toincrease the conversion efficiency of the fluorescent material 903 bywidely and thinly applying the fluorescent material, thereby improvingthe emission luminance.

While the present invention has been disclosed in terms of the preferredembodiment in order to facilitate better understanding thereof, itshould be appreciated that the invention can be embodied in various wayswithout departing from the principle of the invention. Therefore, theinvention should be understood to include all possible embodiments andmodification to the shown embodiments which can be embodied withoutdeparting from the principle of the invention as set forth in theappended claims.

What is claimed is:
 1. A semiconductor light emitting device comprising: a semiconductor light emitting element which has an active layer for emitting primary light having a first wavelength by current injection; a reflector for reflecting said primary light emitted from said semiconductor light emitting element; and a fluorescent material which is applied on part of said reflector and which is excited by said primary light for emitting secondary light having a second wavelength different from said first wavelength, wherein said semiconductor light emitting element and said reflector are integrally formed via a transparent medium having a transparency to said primary light and said secondary light and wherein said reflector is in a shape of a U-shaped recess, and said transparent medium fills in said U-shaped recess.
 2. A semiconductor light emitting device comprising: a semiconductor light emitting element which has an active layer for emitting primary light having a first wavelength by current injection; a reflector for reflecting said primary light emitted from said semiconductor light emitting element; and a fluorescent material which is applied on part of said reflector and which is excited by said primary light for emitting secondary light having a second wavelength different from said first wavelength, wherein said semiconductor light emitting element and said reflector are integrally formed via a transparent medium having a transparency to said primary light and said secondary light and wherein said transparent medium is located between said reflector and said semiconductor light emitting element, so that said reflector and said semiconductor light emitting element are separated on each other.
 3. A semiconductor light emitting device as set forth in claim 1, wherein said transparent medium is located between said reflector and said semiconductor light emitting element so that said reflector and said semiconductor light emitting element are separated from each other.
 4. A semiconductor light emitting device comprising: a semiconductor light emitting element which has an active lay for emitting primary light having a first wavelength by current injection; a reflector for reflecting said primary light emitted from said semiconductor light emitting element; and a fluorescent material which is applied on part said reflector and which is excited by said primary light for emitting secondary light having a second wavelength different from said first wavelength, wherein said semiconductor light emitting element and said reflector are integrally formed via a transparent medium having a transparency to said primary light and said secondary light and wherein said transparent medium is a mold resin.
 5. A semiconductor light emitting device comprising: a semiconductor light emitting element which has an active layer for emitting primary light having a first wavelength by current injection; a reflector for reflecting said primary light emitted from said semiconductor light emitting element; and a fluorescent material which is applied on part of said reflector and which is excited by said primary light for emitting secondary light having a second wavelength different from said first wavelength, wherein said semiconductor light emitting element and said reflector are integrally formed via a transparent medium having a transparency to said primary light and said secondary light and wherein said primary light is a blue light, and said secondary light is a yellow light.
 6. A semiconductor light emitting device forth in claim 5, wherein said active layer is a GaN active layer, and said fluorescent material is YAG: Ce.
 7. A semiconductor light emitting device comprising: a semiconductor light emitting element including: a substrate having a first and second surfaces being opposed to each other, and having a transparency to primary light having first wavelength; a buffer layer formed on the second surface of said substrate; a first conductive type semiconductor layer formed on said buffer layer; an active layer formed on said first conductive type semiconductor layer, and emitting the primary light; and a second conductive type semiconductor layer formed on said active layer; a reflector for reflecting said primary light emitted from said semiconductor light emitting element; a fluorescent material which is applied on part of said reflector and which is excited by said primary light for emitting secondary light having a second wavelength different from said first wavelength; and a transparent medium, via which said semiconductor light emitting element and said reflector are integrally formed, said transparent medium having a transparency to said primary light and said secondary light and wherein said reflector is in a shape of a U-shaped recess, and said transparent medium fills in the U-shaped recess.
 8. A semiconductor light emitting device comprising: a semiconductor light emitting element including: a substrate having a first and second surfaces being opposed to each other, and having a transparency to primary light having first wavelength; a buffer layer formed on the second surface of said substrate; a first conductive type semiconductor layer formed n said buffer layer; an active layer formed on said first conductive type semiconductor layer, and emitting the primary light; and a second conductive type semiconductor layer formed on said active layer; a reflector for reflecting said primary light emitted from said semiconductor light emitting element; a fluorescent material which is applied on part of said reflector and which is excited by said primary light for emitting secondary light having a second wavelength different from said first wavelength; and a transparent medium, via which said semiconductor light emitting element and said reflector are integrally formed, said transparent medium having a transparency to said primary light and said secondary light and wherein said transparent medium is located between said reflector and said semiconductor light emitting element, so that said reflector and said semiconductor light emitting device are separated from each other.
 9. A semiconductor light emitting device as set forth in claim 7, wherein said transparent medium is located between said reflector and said semiconductor light emitting element, so that said reflector and said semiconductor light emitting element are separated from each other.
 10. A semiconductor light emitting device comprising: a semiconductor light emitting element including: a substrate having a first and second surfaces being opposed to each other, and having a transparency to primary light having a first wavelength; a buffer layer formed on the second surface of said substrate; a first conductive type semiconductor layer formed on said buffer layer; an active layer formed on said first conductive type semiconductor layer, and emitting the primary light; and a second conductive type semiconductor layer formed on said active layer; a reflector for reflecting said primary light emitted from said semiconductor light emitting element; a fluorescent material which is applied on part of said reflector and which is excited by said primary light for emitting secondary light having a second wavelength different from said first wavelength; and a transparent medium, via which said semiconductor light emitting element and said reflector are integrally formed, said transparent medium having a transparency to said primary light and said secondary light and wherein said transparent medium is a mold resin.
 11. A semiconductor light emitting device comprising: a semiconductor light emitting element including: a substrate having a first and second surfaces being opposed to each other, and having a transparency to primary light having first wavelength; a buffer layer formed on the second surface of said substrate; a first conductive type semiconductor layer formed n said buffer layer; an active layer formed on said first conductive type semiconductor layer, and emitting the primary light; and a second conductive type semiconductor layer formed on said active layer; a reflector for reflecting said primary light emitted from said semiconductor light emitting element; a fluorescent material which is applied on part of said reflector and which is excited by said primary light for emitting secondary light having a second wavelength different from said first wavelength; and a transparent medium, via which said semiconductor light emitting element and said reflector are integrally formed, said transparent medium having a transparency to said primary light and said secondary light and wherein said primary light is a blue light, and said secondary light is a yellow light.
 12. A semiconductor light emitting device as set forth in claim 11, wherein said active layer is a GaN active layer, and said fluorescent material is YAG: Ce. 